This invention relates generally to the storage, processing and transmission of image information and specifically to a method for efficiently encoding color image information to be displayed or printed.
Color images are conventionally encoded and processed in display or printing systems by parsing the images into component signals and operating on those component signals. In raster-type display systems, it is common to parse color image information into a number of pixels and to provide separate R, G and B signals corresponding to the red, green and blue components of each pixel, respectively. Another common method is to parse the image information into pixels and to provide separate y, u and v signals defining the luminance, hue and saturation of the image.
Digital representation of color images is typically accomplished by representing each pixel of an image by an encoded binary number. It is commonly thought that 256 levels each of red, green and blue information are required to adequately represent the entire visual range to the human eye. Therefore, it is common to assign eight bits to each of the R, G and B signals to form a 24-bit digital word conveying the information for each pixel.
However, it is comparatively more difficult to process 24-bit pixel information than it is to process pixel information that uses fewer bits. Where computing capability is somewhat limited, fewer bits will sometimes be used at the expense of image quality.
Use of a lower pixel depth (number of bits per pixel) affects different types of images or image portions differently. For some image portions, there may be little noticeable difference between a 24-bit pixel depth and an eight-bit pixel depth. For others image portions, the difference in image quality may be significant.